This invention relates to an apparatus for pressure die casting of metals and alloys involving the action of increased gas pressure on the solidifying melt.
In a known apparatus for pressure die casting of metals and alloys, the die is connected to the ram of the machine (i.e., the pressing piston) by means of a pneumatic piston, which is disposed within a pneumatic cylinder, while the compressing space in front of the pneumatic piston is connected to the cavities of the die, into which pressurized gas is delivered through gas conduits. At least one adjustable check valve is provided in the arrangement, which can be opened to vent the compression space in front of the pneumatic piston, acting towards the cavities of the die (see Bulgarian Pat. No. 21,077).
Drawbacks of this known apparatus are: the reduction of the usable stroke of the machine (i.e., the press) because of the inclusion of an additional unit, i.e., a pneumatic cylinder with piston, between the pressing piston and the die; the insecure guiding of the die during operation because of the movable connection between it and the pressing piston; and the requirement of first having to close the die and only then to begin the compression of the gas.
Another known apparatus for pressure die casting with increased gas pressure is a specialized hydraulic press with separate devices for closing the die and for pressing. It is provided with an independent hydro-pneumatic multiplier, disposed within the pressing piston and connected by means of corresponding valves to a supply reservoir for gas and to the die cavity. Only after closing of the die is there actuated the multiplier for increasing the pressure of the gas within the die cavity to the necessary level.
The drawbacks of this apparatus lie in its complicated design and in the impossibility to apply a high gas pressure immediately after the closing of the die.